IMMUNOMONITORING LABORATORY (IML) SHARED RESOURCE: PROJECT SUMMARY The Immunomonitoring Laboratory (IML) is a shared resource (SR) facility within the Bursky Center for Human Immunology and Immunotherapy Programs established in 2013. The IML provides the structure, instrumentation, and expertise to monitor the impact of specific immunotherapies on patient immunologic profiles, interrogate mechanisms and pathways related to treatment protocols, and advance the conceptual basis for targeted treatment strategies. In addition, the IML monitors developing immune responses to new therapies in animal models of cancer treatment to elucidate novel therapeutic strategies or develop unique processes to evaluate treatment outcomes in translational studies and new clinical trials. The IML is composed of four integrated groups that include cytometry (conventional flow cytometry analyses, mass cytometry [CyTOF2], and imaging mass cytometry), immune monitoring (multiplex analysis and functional assays), custom tetramer development (currently with an inventory of over 50 HLA alleles), and tissue processing related to IML projects. The IML has recently brought on board two imaging technologies: a Hyperion CyTOF capable of detecting > 40 distinct metal- labeled biomarkers from tissue sections and a CODEX system that can visualize >40 unique DNA barcoded biomarkers from frozen or FFPE sections using light microscopy. These two state-of-the-art technologies will allow investigators to visualize the spatial orientation of interacting immune, stromal, and tumor components and allow scientists to see the interaction between cells and understand the molecular and cellular basis of complex diseases that arise as these interactions become abnormal. In the current project period, the IML has grown the number of laboratories serviced by 3-fold and more than doubled the number of Siteman Cancer Center (SCC) users, along with supporting a number of ongoing clinical trials. The IML continues to acquire new technologies as specialized tools become available to meet the needs of our Washington University (WU), SCC, and Barnes-Jewish Hospital (BJH) clinicians and scientists. In addition to our new Hyperion and CODEX technologies, the IML is currently developing MHC class II tetramers that will be available in the coming months to track and quantitate antigen specific CD4 T cells in response to immunotherapy. In addition, the IML is actively working with other institutions to harmonize validation assays for tetramer staining of patient samples. The IML works to customize assays for maximal data recovery from rare samples, has the flexibility to develop new protocols, and has been responsive to calls for the newest technologies to support our clinicians and scientists.